I’m guessing they are looking for a lot more detail with the 3 meter cores - changes in life forms, etc. At least it isn’t the 2 FOOT cores they use on shallow environmental jobs!
I worked on an oil rig back in college. One time we spent all day coming out of a hole. Went to bed dead-tired, but knowing that when we got up the other crew would finish and we would have an easy day.
Woke up and looked out the window to a rig with a lot of pipe still on the stack! The other driller lost count and slammed the drill bit into the bottom of the well. We had to continue tripping out of the hole to replace the broken bit! Aaaaggggghhh!
The reasons not to: Unconsolidated material, and a high risk of losing core, running a core barrel with a sleeve designed for unconsolidated material, which is a shorter core barrel, but has a better recovery rate in unconsolidated sediment (or highly fractured rock).
Or they figure the fractured rock will slide along the fracture planes while coring and jam the inner barrel, at which point one of two things happens--
You either continue to your full barrel depth and grind up the core from the point where you jammed the barrel...
... or You stop coring anyway, because the rock will not slide up the inner barrel and that supports the weight you are trying to put on the bit (which can no longer cut the rock below it).
In the first case you think you are coring, but you lost data instead.
In the second, you just aren't going any farther and end up tripping anyway.
I have seen both events in the years I have spent in the patch.
(And yes, I have seen a number of expensive screw-ups happen, too).